As an injector that injects fuel into cylinders of an internal-combustion engine, the injector that integrates a sensor device therein, which detects a pressure of fuel, is proposed (refer to Japanese Patent Application Laid-Open Publication No. 2010-242574, For example).
A common sensor device 2 shown in FIGS. 4A and 4B, for example, has a housing 21 screwed to an injector body. A male screw 211 is formed on the housing 21, as well as an engaging part 213 in which a jig that rotates the housing 21 is engaged is formed in the housing 21.
Moreover, an electric circuit unit such as a mold IC 23 is disposed in the housing 21 at an end side in a direction of a rotational axis X of the housing 21.
Further, a circle A shown with a dashed line in FIG. 4B is a circumscribed circle of the engaging part 213, and the engaging part 213 has a shape of regular polygon close to a circle (dodecagon, for example) when seen along the direction of the rotational axis X of the housing 21.
Moreover, the mold IC 23 is formed into a shape as circularly as possible when seen along the direction of the rotational axis X of the housing 21, and is arranged in a projected plane of the engaging part 213.
However, if the mold IC 23 does not have the shape close to the circle but a shape close to a square, the substantially square-shaped mold IC 23 is to be disposed in the projected plane of the engaging part 213 that has the shape of regular polygon close to the circle, thus wasting space.
Thereby, a whole structure of the injector becomes large and it brings a result on which a marketability of a product is dropped.